LCD Repair Tips

[lilshawn]

With the sunset of CRTs and the dawn of LCD long but passed, LCD screens are beginning to be at high noon of existence. Sooner or later every one of you will experience failure of their LCD of one sort or another. While it seems like it's not for the faint of heart, it's actually pretty easy to repair them.

Most of you will experience CAP FAILURE...
Charicterized by: a flashing indicator light, the powersupply is trying to start up but can't because it's overloaded by blown caps.

The solution: easy! replace the failed caps. most of us have done this already.

Why this happens: The power supply has a 5 volt power supply running all the time. (even when off) it's usually this cap that needs replacing...but replace them all!

The fix: upping the voltage of the caps seems to help them last much much longer. cooling helps even more. try to remove any covers and shielding if you can to help airflow. it gets hot and stuffy in there. Caps are often smashed next to each other and up against heatsinks. Try relocating them or laying them down out of the way so there is plenty of air to take the heat away.




Other failures are caused by a FAILED BACKLIGHT INVERTER

Charicterized by: No picture on screen but power indicator light is on. Picture comes up for a few seconds to few minutes then blips off (indicator light stays on)

The solution: The problem is cause by defective inverter. Sometimes they can be fixed, but often it's the MOSFET switchers that fail. replace the inverter board is the easiest way. Sometimes the inverter board is part of the main powersupply. while unfortunate, you must replace the whole board. Repairing these inverters is a real pain in the butt since they often utilize surface mounted components, repair is very difficult.

Why this happens: again your enemy is heat. Often these inverters are covered in plastic covers. While useful for keeping the Chinese makers from being zapped, all this does is hold the heat in. once the covers are in place nobody is going to be touching it.

The fix: once again removing any shielding or plastic covers holding heat in will help cool things down. The inverter is a very hard working piece of electronics...similar to a HOT it has to switch thousands of times a second. Heat is bad.





Still other failures are caused by FAILED BACKLIGHTS

Charicterized by: Display is dim or dark, but you can still readable. The display has a pinkish or blueish tint that slowly gets better as the display warms up. a corner/side/half of the display is dark while the other(s) are fine.

The solution: Replace the CCFL backlight lamps. (and inverter...see below)

Why this happens: The tube isn't lighting up. This is either due to physical damage (broken) or the electrodes are worn out. (possibly due to failing inverter)

The fix: The tube(s) need to be replaced you will need to disassemble the panel to get to them. if your time is worth anything, it's often best to go ahead and replace the monitor as this will take several hours. The tubes have electrodes at either end. If the electrodes get wore out it's usually because the inverter is failing. The inverter uses a very high voltage spike to light the tube initally (called "striking" the tube.) once the tube is lit it uses a lower voltage to maintain the arc. Failed inverters (or poorly designed ones) will keep dumping the higher voltage into the tube causing the electrodes to erode away. It's best to replace the inverter as well as the tubes.



While not all inclusive, FAILED POWER SUPPLY

Charicterized by: no display no powerlight no nothing.

The solution: Replace or repair the power supply

Why this happens: The powersupply is usually pretty a simple switchmode power supply. it supplies 5 and 12 volts (usually) there is only a few items that fail. But when they do it often takes out several components, making complete repair difficult. Power surges are the biggest culprit. They often take out the fuse and the bridge rectifier. Replacing the failed parts often fixes the supply. I know it sounds obvious what i just said, but sometimes the most obvious answer is the right one. If there is torched parts, replace the supply in it's entirety.

The fix: surge suppressors. Yes they get old, Yes buy good ones, YES YOU PAY WHAT YOU GET FOR. anyone who barebacks the powerline is asking for electrical AIDS. Surge suppressors are only good to filter out so many surges before they start letting then sneak through. Do yourself a favor and buy the expensive APC ones that have a connected equipment policy. even if lightning strikes your house and blows up your whole computer, APC will buy you a new one.




With all that said, I have previously purchased parts from www.lcdparts.net

Note that i'm not affiliated with them in any way. They just happen to have about 90% of the parts i had been looking for, and at a very reasonable price.

[mgb]

Very good info,
Thanks for sharing that lilshawn.

[lilshawn]

I'll post up some pics as I get some crapped out monitors come in for service.

The last batch of monitors I fixed (
1 had faulty backlights (replaced inverters - lamp replacement for this monitor was cost prohibitive.)
2 had faulty inverters (replaced inverters)
2 had faulty power supplies (new caps)
1 had a faulty touch screen panel (replaced overlay)
1 had a faulty touch panel (fixed with a good cleaning)
1 had a misconfigured touch controller (someone swapped a controller from a 17" monitor and installed it in a 19" without setting the jumper on it for the larger panel.)

but i was too busy fixing to take photos which is why I wrote this little diddy up.

[mgb]

This kinda info is good because I think a lot of people either get mystified by some newer technology and think they can't repair it or they think, well its throw away so I must not be able to work on it.

I have only worked on one LCD so far and that was a 32" tv that the picture all of a sudden went shot on. It looked like the pic you get if you set your pc display settings to the lowest res and color pallette. It forced me to learn alittle about the components of an lcd tv and in the end, the fix just involved opening it up and reseating all ribbon cables. Its been working great now for over a year.

Quick question, I don't suppose there is any fix for a single bad pixel os there? Other than replacing the display panel that is?

[lilshawn]

bad as in black

or bad as in stuck on all the time.

sometimes you can use a soft cloth and gently rub around the affected pixel and get it to start working again.

sometimes this can work too: http://flexcode.org/lcd.html

[mgb]

Its always blue so I guess its on

[HaRuMaN]

I had weird lines on a screen of mine, and a hissing sound upon startup.  Opened it up, bad caps.  You could see them bulging and leaking.  Replaced the caps, works perfect now.  Like $5 in parts.   

[lilshawn]

electrical hiss is really a good indicator of failed caps. Thanks for reminding me HaRuMaN

everything from power supplies to router to... anything really.

your internet dropping out? pick up your modem or router hold it up to your ear and give it a listen. 

[Vigo]

Great info! 

I've only run into bad CCFL tubes/bad inverter and replaced them before. Like Lilshawn posted, it might just be an easier fix to replace the whole monitor. Since it is a really good idea to replace the inverter as well, you could be looking at a price starting at $30 for 2 CCFL tubes and a standalone inverter. A lot depends on the size of monitor though. I never bought an inverter that is specifically for my monitor because in every case it was shelling out a lot of money. So, I've had to externally mount the standalone inverters on the back of the monitor casing. If you are willing to putz around with the monitor, it can still be saved, but a replacement craigslist monitor might cost the same or less if you are not too attached to your monitor.

As a side note, CCFL tubes break really easily and might have an unshielded wire running to the far end if both wires meet on the same side of the tube. Getting zapped by touching the bare wiring or the electrodes will hurt a lot. It might even leave a welt. It is best to be careful when working with CCFL tubes.

[lilshawn]

Getting zapped by touching the bare wiring or the electrodes will hurt a lot. It might even leave a welt. It is best to be careful when working with CCFL tubes.

been there, done that...in fact with this last batch of monitors I fixed . I was placing some shielding foil down to protect the touchscreen cable from interference from the inverter and ran my finger past the connector for the lamp. The electricirty arced out from the bare conductor inside the plastic connector and zapped my finger.

no welt or nothing (I got pretty thick skin on my fingers) a little bit of a sting, but you could smell a little bit of hotdog 

so yeah...get everything together THEN test it.

I was running it powered so I could be sure there was no interference from the inverter where I was running the cable.

DO AS I SAY NOT AS I DO. 

[sharpfork]

So the default answer for arcade monitor trouble remains "a cap kit."

I've had success replacing power supply caps in a wide range of LCDs in recent years.  I had my first no fix last night = booo! 

[lilshawn]

So the default answer for arcade monitor trouble remains "a cap kit."

I've had success replacing power supply caps in a wide range of LCDs in recent years.  I had my first no fix last night = booo! 

often what happens is the caps go, but the monitor will continue to run. basically the monitor is running straight off the regulators. (usually a good sign that the designers over engineered the supply) the regulators will run super hot until they fail. then you are looking at a whole new monitor because when the regulators fail they usually short. this is BAAAD because unregulated power shoots into the main decoder board and fries it.

keep on the lookout for unusual signs... things like when you hit the power it takes a longer than normal. 3 seconds versus 2 seconds I would consider abnormal. or maybe a powerlight that comes on then dims down a little bit before the monitor comes up. these are the kind of things that indicate the powersupply is having a hard time coping with the increased load of  dead caps.

[Rick]

Dude, I am so here now. Thanks so much! (You wouldn't want to share your tricks and tips for where best to find 'semi' broken LCD's, would you? Maybe outside the back dumpster of your local Best Buy/Future Shop?)

[lilshawn]

government surplus auctions. stuff can be had for cheap cheap. i just bought a pallet 20 LCD monitors for $10. in varying states of quality/operation.

dumpsters (obviously) key areas to check...apartment buildings. 200 families sharing a single dumpster...check several times a week till you know which days they pick up. check around holidays where new electronics are given...fathers day, christmas etc. you can get working stuff lots of times.

find your local amusement or audio video company. their dumpster will be full of all kinds of good stuff. especially companies who install tvs for bars and lounges. they have a problem...if something is used for a commercial purpose, it's warranty is void....if they buy it under the company name (for tax bookkeeping) they can't RMA it, so they have to throw them out. often they have no time to fix stuff like that, so they toss them.

[ed12]

welp as i do a fair share of lcd and plasma repair

yes caps #1
inverter's #2
on a plasma u find a bad driver board
refer to the x or y subtain board as 1 is blowen and pulling the power-supply down
tcon is easy
sound no pic..tcon board
these are eazy gidits once u get the hang of them
for other note's on 90% of lcd's i try to place 2 fan's in
2" job's do perfect,keep's then running colder
when i do cap's 100% of the time
i do not cheap out
110c is the min i will put in
plus in the switch power supply's i demand low esr caps
or i will not repair it
just food to think on

ed

[Rick]

government surplus auctions.
dumpsters (obviously) find your local amusement or audio video company.

o.O

Omg man. Do you do this for a living? That's amazing information. Thanks so much!

[lilshawn]

government surplus auctions.
dumpsters (obviously) find your local amusement or audio video company.

o.O

Omg man. Do you do this for a living? That's amazing information. Thanks so much!

yyyyyy-yes.